Recent years have witnessed practical use of a flat-panel display in various products and fields. This has led to a demand for a flat-panel display that is larger in size, that achieves higher image quality, and that consumes less power.
Under such circumstances, great attention has been drawn to an organic electroluminescent (hereinafter abbreviated to “EL”) display device that (i) includes an organic EL element which uses electroluminescence of an organic material and that (ii) is an all-solid-state flat-panel display which is excellent in, for example, low-voltage driving, high-speed response, and self-emitting.
An active matrix organic EL display device includes, for example, (i) a substrate made up of members such as a glass substrate and TFTs (thin film transistors) provided on the glass substrate and (ii) thin film organic EL elements provided on the substrate and electrically connected to the TFTs.
A full-color organic EL display device typically includes organic EL elements of red (R), green (G), and blue (B) as sub-pixels aligned on a substrate. A full-color organic EL display device carries out an image display by, with use of TFTs, selectively causing the organic EL elements to each emit light with a desired luminance.
Thus, such an organic EL display device needs to be produced through at least a process that forms, for each organic EL element, a luminescent layer having a predetermined pattern and made of an organic luminescent material which emits light of one of the above three colors.
Examples of known methods for forming such a luminescent layer having a predetermined pattern include a vacuum vapor deposition method, an inkjet method, and a laser transfer method. For example, the vacuum vapor deposition method is mainly used for a low-molecular organic EL display device (OLED) to pattern a luminescent layer.
The vacuum vapor deposition method uses a vapor deposition mask (also referred to as a shadow mask) having openings each having a predetermined pattern. A thin film having a predetermined pattern is formed by vapor-depositing vapor deposition particles (vapor deposition material, film formation material) from a vapor deposition source onto a vapor deposition target surface through the openings of the vapor deposition mask. In this case, the vapor deposition is carried out for each color of the luminescent layers (This is referred to as “selective vapor deposition”).
The vacuum vapor-deposition method is roughly classified into two methods: (i) a method for forming a film while fixing or sequentially moving a film formation target substrate and a vapor-deposition mask so that the film formation target substrate and the vapor-deposition mask are brought into close contact with each other; and (ii) a scanning vapor-deposition method for forming a film while scanning a film formation target substrate and a vapor-deposition mask that are separated from each other.
The former method (i) uses a vapor deposition mask equivalent in size to a film formation target substrate. However, use of the vapor deposition mask equivalent in size to the film formation target substrate requires the vapor deposition mask to be larger in size as the film formation target substrate is larger in size. Such an increase in size of the film formation target substrate accordingly easily causes a gap between the film formation target substrate and the vapor deposition mask due to self-weight bending and extension of the vapor deposition mask. Therefore, with a large-sized substrate in use, it is difficult to carry out patterning with high accuracy, and there will occur positional displacement of vapor deposition and/or color mixture. This makes it difficult to form a high-definition vapor-deposition pattern.
Further, as the film formation target substrate is larger in size, not only the vapor deposition mask but also a frame, for example, that holds the vapor deposition mask and the like is enormously larger in size and weight. Thus, the increase in size of the film formation target substrate makes it difficult to handle, for example, the vapor deposition mask and the frame. This may cause a problem with productivity and/or safety. Further, a vapor deposition device itself and its accompanying devices are also larger in size and complicated. This makes device design difficult and increases installation cost.
In view of the problems, great attention has recently been drawn to a scan vapor deposition method for carrying out vapor deposition while carrying out scanning (scan vapor deposition) by use of a vapor deposition mask which is smaller than a film formation target substrate.
According to such a scan vapor deposition method, a band-shaped vapor deposition mask, for example, is used, and that vapor deposition mask is, for example, integrated with a vapor deposition source. Then, vapor deposition particles are vapor-deposited on an entire surface of a film formation target substrate while at least one of (i) the film formation target substrate and (ii) the combination of the vapor deposition mask and the vapor deposition source is moved relative to the other.
Thus, the scan vapor deposition method, which makes it unnecessary to use the vapor deposition mask equivalent in size to the film formation target substrate, can solve the above problems that uniquely occur when a large-sized vapor deposition mask is used.
The scanning vapor-deposition method typically involves a vapor deposition source having a plurality of emission holes (nozzles) so arranged at a predetermined pitch in a direction perpendicular to the scanning direction as to allow vapor deposition particles to be emitted (scattered) as a vapor deposition material is heated for evaporation or sublimation.
There have thus been proposed in recent years methods of limiting vapor deposition flows (that is, flows of vapor deposition particles) with use of limiting plates for scan vapor deposition so that vapor deposition particles emitted from a nozzle will not fly toward a vapor deposition region (film formation region) adjacent to a corresponding vapor deposition region, toward which adjacent vapor deposition region vapor deposition particles emitted from an adjacent nozzle fly.
Patent Literature 1 discloses, for example, that a blocking wall assembly is provided on one side of a vapor deposition source, the blocking wall assembly including, as limiting plates, a plurality of blocking walls partitioning a space between the vapor deposition source and a vapor deposition mask into a plurality of vapor deposition spaces. According to Patent Literature 1, since the blocking walls, serving as limiting plates, limit a vapor deposition range, it is possible to vapor-deposit a pattern with high definition while preventing spread of a vapor deposition pattern.
Japanese Patent Application Publication, Tokukai, No. 2010-270396 A (Publication Date: Dec. 2, 2010)